1. Field of the Invention
The present invention relates to a steering control system for causing a moving vehicle such as an automobile, a driverless mobile and carrying device in a factory, or a vehicle used in agriculture, civil engineering machinery and the like, to travel along a preset course, and is more particularly concerned with a steering control system for causing such a moving vehicle to detour around obstacles on the traveling course thereof.
2. Description of the Prior Art
As an example of a conventional control means for steering a moving vehicle as described above along a predetermined course to carry out desired work operations such as grass clipping, transporting and the like, there is a system which includes means for detecting a present position and an advance direction of the vehicle with respect to reference points disposed at at least three positions in and around a work zone, and the traveling direction of the moving vehicle is controlled on the basis of the positional information obtained from the detecting means.
Moreover, as another example of a steering control system, there is a system wherein electromagnetic cables, magnetic tapes or light beam reflecting tapes or the like are disposed along a predetermined course in a work zone, and the direction of a moving vehicle is controlled by detecting the position of the moving vehicle relative to these cables, tapes or the like.
There are also some moving vehicles that include a sensor for detecting whether and where an obstacle or obstacles are present on the predetermined traveling course, and means are provided for detouring the vehicle around the obstacle and along a prescribed detouring pattern when any obstacle is detected. However the steering control in these systems is effected in accordance with a detouring pattern calculated in response to the position of an obstacle, or the vehicle is detoured around the obstacle along a predetermined detouring pattern, and these systems therefore suffer from the disadvantage that the moving vehicle cannot correctly return to the predetermined traveling course after the detouring operation if the moving vehicle gets out of position due to slip and the like of its wheels during the detouring operation.
In an effort to solve the problem described above, Japanese Patent Laid-open No. 47606/1985 discloses an automatically traveling working vehicle (moving vehicle) which comprises an azimuth sensor for detecting deviation in the direction of the vehicle body with respect to a prescribed reference azimuth, and a control means is provided for causing the direction of the vehicle body to coincide with the reference azimuth on the basis of the azimuth detected by the azimuth sensor during travel of the vehicle along a straight portion of a predetermined detouring pattern. This arrangement has, however, given rise to other problems. While deviation of the vehicle from the predetermined course due to slip and the like of its wheels can be corrected during the detouring operation, the correction is based on a predetermined sequence so that the detouring patterns are restricted. Accordingly, the moving vehicle cannot necessarily accomplish the detouring operation in an efficient manner by passing through the shortest course with respect to obstacles which have various dimensions. In addition the area where the moving vehicle has gone around an obstacle is left as an unfinished working place. In order to complete the desired working operation on such a leftover zone, either the obstacle was removed and then the moving vehicle was transferred back to the position where the obstacle had been present by manual control, radio control or the like so that the vehicle could resume the prescribed working operation, or the prescribed working operation was completed manually on the unfinished working place. Since the automatic operation was frequently interrupted by such manual operations, expected advantages were not obtained in spite of the intention that a moving vehicle be used to attain energy saving and to elevate working efficiency.
Furthermore, while it has been arranged in the above described moving vehicle that the direction of the vehicle body is adjusted to its reference azimuth in a straight portion of its traveling route along a detour, no such countermeasure is provided when a positional deviation appears while the vehicle is following an oblique travel course.